Condensed Matter > Mesoscale and Nanoscale Physics

Title:Cooper pair splitting in ballistic ferromagnetic SQUIDs

Abstract: We consider ballistic SQUIDs with spin filtering inside half-metallic
ferromagnetic arms. A singlet Cooper pair cannot pass through an arm in this
case, so the Josephson current is entirely due to the Cooper pair splitting,
with two electrons going to different interferometer arms. In order to
elucidate the mechanisms of Josephson transport due to split Cooper pairs, we
assume the arms to be single-channel wires in the short-junction limit.
Different geometries of the system (determined by the length of the arms and
the phases acquired by quasiparticles during splitting between the arms) lead
to qualitatively different behavior of the SQUID characteristics (the Andreev
levels, the current-phase relation, and the critical Josephson current) as a
function of two control parameters, the external magnetic flux and
misorientation of the two spin filters. The current-phase relation can change
its amplitude and shape, in particular, turning to a pi-junction form or
acquiring additional zero crossings. The critical current can become a
nonmonotonic function of the misorientation of the spin filters and the
magnetic flux (on half of period). Periodicity with respect to the magnetic
flux is doubled, in comparison to conventional SQUIDs.

Comments:

15 pages, 6 figures; identical to the published article. In comparison with the previous version, we added the explanation of how the results in the limiting cases meet each other at the overlap points. The discussion of experimental issues was extended and moved to a separate new Sec. V Discussion